Algae study adds to ‘bleak’ future for polar bears

[USA] New research has suggested “bleak” predictions of a major fall in polar numbers may have been underestimated.

According to the Scottish Association for Marine Science (SAMS), forecasts of a 30 per cent drop over the next four years fail to consider the impact of changes in the food chain that could devastate populations of the Arctic predator.

The Oban-based institute suggests the “bleak” future expected could be far less harsh than the reality.

Scientist Dr Thomas Brown, who specialises in Arctic research, says this is due to the possible impact of alterations in the production of the microscopic algae that underpin the food chain.

The algae, which grows under sea ice, is eaten by zooplankton and the energy eventually “works its way up the food chain to the region’s top predator”.

Analysis of three polar bear populations in the Canadian Arctic – one in Baffin Bay and two in Hudson Bay – shows that an average of 86 per cent of the energy in the animal’s diet is derived from sea ice algae.

Until now, forecasts on the bears’ future have focused on how the reduction of sea ice as a result of warming temperatures will result in a loss of habitat, giving them less room to roam and fewer options for hunting.

Studies have found that the level of sea ice cover in the Arctic Circle is falling year on year, with the lowest winter maximum ice extent ever seen recorded last March. However, Brown says his findings highlight another growing problem, with the threat to the algae that underpins the food chain also posing a concern to the region’s “entire food web”.

The claims rely on a method devised by Brown to measure how much of a species’ diet is derived from Arctic sea ice.

It traces a chemical produced by the algae, known as IP25, all the way up the food chain.

Brown, whose work has been published in the journal PLOS One, said: “Polar bears rely on sea ice as their habitat.

“Consequently, conservation assessments of polar bears identify the ongoing reduction in sea ice to represent a significant threat to their survival.

“However, the additional role of sea ice as an indirect source of energy to bears has been overlooked.”

He went on: “The polar bears’ reliance on carbon [energy] derived from sea ice algae was surprisingly high and shows that the reduction of sea ice means more than just a loss of habitat.

“It threatens the success of the entire food web in the Arctic as we know it.”

Brown continued: “We know that carbon from sea ice algae is important for Arctic animals, but we need to quantify how much of that carbon is consumed in order to understand the full impact of sea ice loss.”

The scientist believes his algae measuring method could inform future conservation methods through the method of long term monitoring of polar bear diets